Issue Turning Template into Variadic Template

[H. S. Teoh via Digitalmars-d-learn]

On Wed, Mar 30, 2016 at 08:43:03PM +0000, jmh530 via Digitalmars-d-learn wrote:
> On Wednesday, 30 March 2016 at 18:56:29 UTC, H. S. Teoh wrote:
> >
> >Does this do what you want?
> >
> 
> Okay, I've looked at this a bit more thoroughly and it works perfectly
> (perhaps with a better name put in phobos?).
> 
> If I'm understanding this correctly, the ImplType creates the correct
> type signature for the output and then conditionalOnly puts the right
> value in.

Yes.

It was a quick hack, though, and involves assigning the ranges to a
local variable.  There ought to be a way to pass the arguments directly,
while substituting the non-ranges with only(x).  But that would probably
involve even more black magic that I'm already invoking. :-P  It's
pretty close to the point where I'd just throw up my hands and say,
forget the template black magic shenanigans, just write a mixin and call
it a day.


> One thing that is confusing is that when I create a new function that
> adjusts conditionalOnly to just return y instead of fun(y), then I get
> an error about returning a tuple. I'm like, where did I use a tuple. I
> guess related to https://issues.dlang.org/show_bug.cgi?id=15436

Yes... basically the compiler is complaining that it doesn't know how to
return a value with of AliasSeq type.  Why it can't do this, is a
complex question that I don't have the time to get into right now... but
basically, if you want to return it instead of calling the target
function, you have to wrap it in a std.typecons.Tuple struct (how's that
for confusing terminology?!), and use .expand to unwrap it when you need
to pass it to a function.


T

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